Biofouling is a major concern with modern desalination membranes (e.g., reverse osmosis (RO) or nanofiltration (NF) membranes) because it cannot be easily eliminated and plagues many applications such as seawater and brackish water desalination, as well as conventional water and wastewater treatment. A breakthrough in the field of membrane separations was the development of thin film composite membranes, which are characterized by an ultra-thin “barrier” layer supported on a porous substrate. Among thin film composite membranes, polyamide thin film composite membranes have been widely commercialized for water purification applications such as seawater desalination, surface water treatment, and wastewater reclamation due to their excellent separation performance and energy efficiency.
In recent years, the water permeability of conventional polyamide thin film composite membranes has improved dramatically without an appreciable change in solute rejection. Polyamide thin film composite membranes are widely commercialized for use in RO separations such as seawater desalination, water treatment, and wastewater reclamation due to their excellent membrane selectivity. Despite this advantage, one concern with conventional polyamide (PA) thin film composite (TFC) membranes in these applications is their loss of performance due to biofouling, which typically cannot be eliminated by feed water pretreatment, membrane surface modification, module and process optimization, or chemical cleaning. S. Kang et al., Direct Observation of Biofouling in Cross-flow Microfiltration: Mechanisms of Deposition and Release, Journal of Membrane Science 244 (2004) 151. A small amount of microbial deposition can result in extensive biofilm growth, which in RO processes leads to higher operating pressures and more frequent chemical cleanings. This in turn can shorten membrane life and compromise product water quality.
Therefore, there remains a need for methods and compositions that overcome these deficiencies and that effectively provide for membranes having improved fouling resistance, anti-microbial (biocidal) activity, water permeability, and salt rejection.